It is the present state of art that no basic technique has yet been established to permit conversion of an original picture into a reproduced picture with good reproducibility in gradation and tone (hereinafter called "quality") in the tonal conversion of the original picture for the production of the reproduced picture from the original picture.
In other words, in the reproduction of the original picture quality in the reproduced picture, the "nonlinear conversion technique in the density range of a picture" which may be considered to form a basis for the reproduction is dependent totally on experiences and perception of an operator and is thus non-scientific and non-rational.
The term "nonlinear conversion technique in the density range of the picture" (hereinafter called the "conversion technique in the density range of the picture" or merely the "tonal conversion technique of the picture") means a technique which is fundamentally different in field from image processing in the spatial range, image processing in the spatial frequency range, image processing of a given picture by a statistical method, and processing techniques for pictorial characteristics of a given picture such as pattern analyses. It rather provides a basic technique for these image processing technology.
Because, it is the crux, basis and fundamental of the tonal conversion of a picture upon production of a reproduced picture that irrespective of the characteristics of the original picture and irrespective of the technical details or means therefor, the quality of the original picture be converted at the ratio of 1:1 and the quality of the resultant reproduced picture has a suitable density gradient whereby the reproduced picture is felt natural to the visual sensation of man.
However, the present conversion techniques in the density range of a picture (tonal conversion techniques for pictures) are totally dependent on the experiences and perception of man. Moreover, no attempt has been made to improve these techniques to rational and scientific ones. Accordingly, conventional machines, equipment and components for obtaining reproduced pictures on the basis of any of such conventional tonal conversion techniques for pictures as well as conventional systems using in combination two or more of such conventional machines, equipment and components cannot provide reproduced pictures with good reproduction of the quality of original pictures. In addition, their constructions are unnecessarily complex and sophisticated, leading to problems in manufacturing costs, ease and convenience in use, repair, maintenance, etc.
These problems can be attributed primarily to the fact that no tonal conversion technique for a picture, which permits scientific and rational reproduction of the quality of the original picture at the ratio of 1:1 in a reproduced picture, has yet been established as the above-mentioned basic technique in the conversion technology for pictures.
Referring to specific tonal conversion techniques for pictures, this matter will be discussed to a some extent.
(i) Production of printed pictures:
(a) When plate-making work is not standardized, especially, when a printing plate is made using as an original picture a photographic color film picture having non-standard quality (for example, over-exposed or under-exposed color film picture), there is no rational method to cope with the irregularity in quality and the plate-making work has to be conducted depending fully on the experiences and perception of man. A major reason for the lack of development of a scientific approach in this field is the presence of an excuse preventing the search for a rational technique, that is, artistic elements or aspects which inherently accompany printed materials.
(b) If one wants to stabilize the quality of products to increase the productivity of the plate-making work, the construction of a scanner as a plate-making apparatus becomes more complex and more expensive. Moreover, the operation of the scanner becomes more difficult. Thus, a great deal of labor is required for the education and training of its operators.
(c) Even if such a sophisticated and complicated scanner is introduced, 30-40% of color separation work has to be done over again for spoilage or other reasons.
(ii) The more the image processing function is sophisticated, the more the processing speed is increased and/or the more the flexibility to the function is imparted in digital image processing apparatus such as a color copier or in a digital image processing software, the constructions of the software and hardware becomes progressively complex. This results in an increased manufacturing cost and in contrast, in a reduction of flexibility. Further, the reduction of a software to a hardware is rendered more difficult.
(iii) In luminescent pictures such as TV pictures, there is a strong demand for the good reproduction of quality. There is another demand for the development of a simple method for the adjustment of quality. For the manual adjustment of the quality of TV pictures, complex adjustment procedures are required with respect to the brightness, contrast, and the three colors (R, G and B). An automatic control system requires a complex construction and leads to a higher manufacturing cost. Nevertheless, it is the current circumstances that fully satisfactory reproducibility of quality has not attained yet.
(iv) Upon taking a picture in a low illuminance range (dark field) which is a typical example of invisible ranges to the visual sensation of man, a time-related limitation is imposed on the photographing conditions by the moving speed of the object. Even if one tries to eliminate the time-related limitation by a simple amplifier means or the like, it is difficult to obtain a vivid picture excellent in the reproduction of the quality.